Piezo-electric device and method of producing the same



Nov. 24, 1925- A. M L. NICOLSOFL PIEZO ELECTRIC DEVICE AND METHOD OF PRODUCING THE SAME Filed Aug. 1923 Wye/77W": ,4/510/7/2/ .Maabaxz Patented Nov. 24, 1925.

UNITED STATES A 1,562,578 PATENT OFFICE.

A LEXANDEB McL. NICOLSON, OF NEW YORK, N. Y., ASSIGNOR TO WESTERN ELEC- TRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

PIEZO-ELEOTRIC DEVICE AND METHOD OF PRODUCING THE SAME.

Applica'tion filed August 6, 1923. Serial No. 655,800.

To all/whom it may concern:

Be it known that I, ALEXANDER MoL. NIoLsoN, a subject of the King of Great Britain, residing at New York, in the county of New York, State of New York, have invented certain new and useful Improvements in Piezo-Electric .Devices and Methods of Producing the Same, of which the following is a full, clear, concise, and exact description.

This invention relates to piezo-electric devices and methods of producing the same, and aims to provide sensitive, efficient, simple and durable devices of that character, 7 for translating electrical variations into mechanical force variations, andvice versa, such devices being useful in, for instance, the transmission and reception. of telephone currents and the phonographic recording and reproduction 0 sound waves.

In accordance with the invention a piezoelectric crystal, preferably a Rochelle salt crystal havin the composite or'hour-glass structure an having orthogonal electric poles, such as is described in my article on The piezo-electric effect in the composite Rochelle salt crystal, Proceedings of the American Institute of Electrical Engineers,

November, 1919, is provided with electrodes or electrically conducting, charge collecting means in contact with the partsof the crystal which are oppositely electrified when the crystal is stressed, one of the charge collecting means being preferably in intimate contact with the interior of the crystal. For

36 example, the means for collecting the charges from the pyramidal poles or hourglass shaped portions of the crystal may be an electrical conductor or conductors within or passing through those portions and cut- 4 ting various imaginary planes perpendicular to the principal axis of the crystal, that is,

planes parallel to and lying between the bang planes of the crystal.

At the lace where this interior electrode or the lead for connecting it in circuit passes through the surface of the crystal it may occupy a very small portion of that surface,

and therefore it is easy to insure that the leakage resistance along the surface of the crystal from this interior electrode to the charge collecting conductor of opposite sign will be maintained high, as for instance, by

bringing the interior conductor, or its lead,

through the surface of the crystal at a poirt tact may be easily maintained between the electrode and the crystal without any necessity of employing adhesive or clamping means to attach the electrode to'the crystal.

Fig. 1 of the accompanying drawings is a side elevation of a loud speaking telephone receiver embodying one form of the inven- I tion; Fig. 2 is a front elevation of F ig. 1;

Fig.3 is a side elevation of a crystal having an interior electrode of a different form from that shown in Fig. 1; Fig. 4 is a rear elevation of Fig. 3; Fig. 5 is a perspective View of a crystal growing about an interior electrode; and Fig. 6 is a fragmentary view of the crystal of Fig. 5 which has been furnished with an exterior electrode and means for increasing surface leakage resistance between that electrode and the lead for the interior electrode. Referring especially to Figs. 1 and 2, a piezo-electric crystal 10 having the composite structure referred to above is mounted on a base 11. The crystal may be produced ,by methods such as, for instance, those described in the above mentioned A. I. E. E. publication or in myPatents No. 1,414,370, May 2, 1922, method of making piezo-electrical crystals, and No. 1,438,965, Dec. 19, 1922, piezo-electric devices and methods of producing the same. Attached to the upper end or upper basal plane of the crystal is an-arm 12 which carries a diaphragm 13' to .be vibrated by arm 12 in response to twisting of the crystal about itsprincipal, or vertical axis. The crystal may be caused to twist byapplying an electromotive force to a girdle electrode 14 and an electrode 15 which is imbedded in the crystal. j Conversely, electromotive force may be generated'between these electrodes by twisting the crystal,.as for instance by causing sound .waves to impinge upon the diaphragm 13.

The girdle electrode is shown as of the character described in the A. I. E. E. publication mentioned above, and also described in the above mentioned Patent No. 1,438,965.

The pyramidal, or hour-glass shaped poles of the crystal are designated lfi and 17 and are indicated in the drawing by dottedlines 18 converging toward the seedling 19 from which the crystal is grown. The interior electrode 15 preferably passes through the pyramids-16 and 17 in the general direction of the principal axis of the crystal and extends substantially the whole length of the crystal, so that it will cut imaginary planes passed perpendicular to the crystal axis and lying between the apices of the pyramids and points near the ends of the crystal. The portion of pyramidal pole lying between any one of these planes and the apex of the pyramidal pole may be regarded as a pyramidal pole having that plane as its basal plane, and the electrode 15 passes through and contacts with a great number of such planes, thus collecting the electrical charges appearing on them when the crystal is stressed, and conducting such charges to the outside of the crystal by means of the lead connected to or forming an extension of the conductor 15, it being understood, of course, that lead 25 may be connected to one terminal of areceiving apparatus (not shown) the other terminal of which may be connected to a lead 27 brought from the girdle electrode 14 of the crystal. When the crystal device is used as a receiver, the source of electromotive force (not shown) from which it is to be operated is connected between leads 25 and 27, and the conductor 15 acts as a charging means, instead of as a collector of electrical charges.

In order to insert the conductor 15 in the crystal, a hole may be drilled in the crystal. The electrode 15 is preferably of some form designed to have intimate contact with the surrounding crystal, and may be, for instance, a column of mercury, saturated Rochelle salt solution, or graphite, or a wire 30 preferably surrounded by tinfoil pellets, graphite, conducting liquid, or other electrically conducting material 31 for insuring that the resistance between the wire and the crystal will be low. The tinfoil pellets, if used, may be tamped in around the wire.

Where the wire 30 passes through the surface of the crystal it may have a rubber covering or other electrical insulation, as indicated at 33, and a tube of quartz or the like having high surface leakage resistance may also surround this portion of the wire 30. Insulating material in the form of a cement is preferably placed around the elements 35, 33 and 30 where they pass through the crystal surface, as indicated at 37. ,A suitable cement may be made by fusing crystalline sodium potassium tartrate. The fused mass may be allowed to cool below the fusion temperature without reams immediate setting, but when thus supercooled will quickly set upon agitation, such for instance as that incident to its applicationto the surfaces which are to be joined. To insure that the cement will have a high resistivity, it should, while in the fused state, be heated sufiiciently long and at a suliiciently high temperature to decrease the water content somewhat, but if heated too long or at too high temperature, the cement, after hardening, will not havesuliiciently strong cohesive and adhesive powers. The cement is preferably also coated over the ends of the crystal, as indicated at 40, to increase the surface leakage resistance between the tube 35 and the girdle electrode 14. It will be seen that any leakage currents flowing from lead 25 over the surface of insulation 33, 35, and 40, and thence over the surface of the crystal to electrode 14, encounter high resistance, so that even in humid weather any effect of this surface leakage resistance in shunting the source or load connected across leads 25 and 27 will be small. This cement and its use in combination with a piezo-electric structure forms no part of the present invention but is claimed inmy copending application, Serial No. 740,746, filed September 30, 1924.

The cement coatings on thetop and bottom ends of the crystal also reduce leakage, over the surface of the crystal, between the basal planes (or bases of the pyramidal portions) of the crystal and the remaining crystal surfaces, because these coatings reduce flow of charge along the surfaces of the basal planes, since the coatings protect the basal planes from exposure to the moisture of the atmosphere, and since the exposed surfaces of the coatings collect relatively little moisture from the air and have high surface leakage resistance even in humid weather. I

The cement coating 40 at the upper end of the crystalmay also be used to cement the arm 12 to the crystal, as indicated in the drawing; and similarly, the cement coating 40 for the lower end of the crystal may be usedto cement the crystal in a groove in the base 11. v

Fig. 3 shows a crystal 10' ofthe same character as the crystal 10 of Figs. 1 and 2, and having a girdle electrode 14 of the same general character as the girdle electrode 14 of crystal 10; but the crystal 10' has two internal electrodes 15' instead of the internal electrode 15 of crystal 10. Two holes are drilled in the crystal 10 for the reception of the electrodes 15', each hole extending from the vicinity of the seedling 19' in the general direction of the axis of one of the pyramidal portions of the crystal, as indi- 15 intersects imaginary planes pendicular to the crystal axis an lying becated by the drawing. Thus, each electrode.

assed perinner end of which the electrodes 15 may be soldered or otherwise electrically connected.

A lead corresponding to the lead 25 in Figs. 1 and 2, may be connected to post 51. The girdle electrode 14 is cut away around the edge of the cement filled recess, as indicated at 55, so that any leakage current flow ing over the surface of the cement 50 between the girdle pole 14' and the leads 2 5" will encounter high leakage resistance on the when the seedling is place exposed surface of the cement 50 even in humid weather. The ends of the crystal 10' may, of course, be capped with cement, as in the case of the crystal 10, and the crystal 10' may be mounted in any suitable manner, as for instance in the manner in which crystal 10 is mounted. To put the electrodes 15' in the crystal 10', the crystal may be turned with its face downward, mercury 31' may be poured "into the holeswhich haye been drilled for it, wires 30' inserted in the'mercury, and cement 50 placed in the recess provided therefor. The wire should preferably be of such character that it will not be easily corroded by the surrounding conductor. Thus, if the surrounding conductoris mercury; for instance, then the wire may be of nickel or iron, for example.

Fig. 5 shows how a crystal may be own about an electrode 61 so that the electrode will be' an interior electrode. The electrode may be given various forms. shown, it consists of a wire like the wire 30 shown in Fig. 1, but having arms 65 extending outwardly therefrom and lying within the pyramidal portions of the crystal. These arms assist the central wire to collect the charges generated in the pyramidal poles when the crystal is stressed. The crystal is grown in the mannerreferred to above, except that the electrode 61 is laid upon the seedling in the osition shown,

if in the mother liquor. As the crystal grows it envelops the electrode 61 in thepyramidal portions of the crystal. The girdle electrode used with this crystal is indicated at in Fig. 6

and may be like that of the crystal 10 of Figs. 1 and 2.

In order to increase the surface leaka e resistance between the'electrode- 61 and t e girdle electrode 7.0, cement of the character referred to above'may be placed around the electrode 61 where it passes through the.

surface of the crystal, as indicated at 175 in Fig. 6; or the electrode 61 may be'brought out by means .of'a cement plug and a binding post, corresponding to elements 50 and- 51 of Fig. 3; or the electrode may be brought out through insulating means of the character shown at 33 and 35 in Fig.

.1. The ends of the crystal 60 may be capped with cement as in the case of the crystal 1 0, and the crystal 60 may be mount: ed in any suitable manner, for instance, as the crystal 1()- is mounted.

What is claimed is:

1. A crystal having means including an electrode in the interior of the crystal, for connecting said crystal in an electric circuit.

2'. A piezo-electric crystal-having means including an electrode in the interior of the crystal, for connecting said crystal in an electric circuit.

- 3. A sodium potassium tartrate crystal having a pyramidal ole, and an electrode extending within said pole. L

4. A piezo-electric crystal comprising two portions oppositely electrified when said crystal is stressed, and an electrode embedded in one of said portions 5. A piezo-electric crystalline structure comprising a pyramidal pole, a girdle pole about said pyramidal 'pole, and an electrode in the interior of said pyramidal pole.

' 6. A piezo-electric crystal comprising a girdle pole and a pole surrounded thereby,

and an electrode interior to said last mentioned pole and emerging from said crystal at a point remote fromsaid girdle pole.

7. A piezo-electric crystal having two adjacent poles of' o posite' sign, an electrode interior to one -0 said poles and having a portion extending through the surface of said crystal and insulated from said crystal.

8. A crystal having an interior electrode, and means for insulating av ortion of said electrode from the surface 0 said crystal.

9. The method of obtaining a crystal with an interior electrode which comprises growing the crystal about the electrode.

10. The method of making a iezo-electric crystal device which comprises growing a sodium potassium tartrate crystal having pyramidal poles and so locating an electrode with respect to the growing crystal as to cause the" electrode to be substantially enveloped in the pyramidal poles by the growth of the crystal. 1

11. A telephone transmitter and receiver comprising a piezo-electric crystal having an interior electrode, an electrode of opposite sign, and means for transmitting elastic vibrations between said crystal and a surrounding medium capable of propagating such vibrations.

In witness whereof, I hereunto subscribe my name this 3rd day of August, A. D.,

ALEXANDER MoL. NICOLSON. 

